The present invention relates to a method for producing bent tubes with a predetermined curved form by a cold drawing operation in which a hollow tube blank has its outer diameter and wall thickness reduced, and an apparatus for carrying out the method.
It is previously known to produce bent tubes, for use as casting moulds, by the drawing of hollow tube blanks but the known methods have generally turned out to be slow and expensive and they have limited the choice of tube material and wall thickness. In many instances the known methods involve uneven quality with undesirable variations in the wall thickness of the tube. Especially in utilizing a bent mandrel, which is inserted into the blank before the drawing operation and is removed after the drawing operation, it has been noticed that the inner surface of the tube has been damaged in connection with the relative motion between the bent mandrel and the tube blank.
The purpose of the present invention is to overcome these inconveniences in the production of tubes by cold drawing over a mandrel.
A further object is to provide a technique which eliminates the disadvantages which are related to bent moulds having a constant radius of curvature, i.e., when such moulds are used for continuous casting relative to the increasing curvature of the cast material when cooled, the cast material will not be in continuous contact with the mould wall.